Display Apparatus

ABSTRACT

A sealing glass of a low melting point glass composition which is a phosphate glass that contains transition metal wherein the glass contains 15 to 35% of BaO and Sb 2 O 3  (in total) and the ratio by weight of BaO to Sb 2 O 3  or Sb 2 O 3  to BaO is 0.3 or less. Particularly the transition metal is vanadium and the glass contains V 2 O 5  of 45 to 60 wt % as vanadium oxide and P 2 O 5  of 15 to 30 wt % as phosphorus oxide.  
     The bonding material is a mixture of a filler and a vanadate-phosphate glass that contains V 2 O 5  as the main ingredient and the glass contains V 2 O 5  of 45 to 60%, P 2 O 5  of 20 to 30%, BaO of 5 to 15%, TeO 2  of 0 to 10%, Sb 2 O 3  of 5 to 10%, and WO 3  of 0 to 5%. The particle size of the filler is in the range of 1 to 150 μm and the ratio of filler is 80% by volume or less of the adhesive glass.

CLAIM OF PRIORITY

The present application claims priority from Japanese applicationsserial No. 2006-154861, filed on Jun. 2, 2006 and serial No. 2007-20308,filed on Jan. 31, 2007, the contents of which are hereby incorporated byreference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to an image display apparatus equippedwith a vacuum space and to a glass bonding material for sealing or glasscomposition for sealing used to produce the display apparatus.

BACKGROUND ART

Recently, information processing apparatus or television apparatus havea tendency to use extended definition functions. So, flat panel display(FPD) apparatus have been in the spotlight since they havehigh-brilliance and high-fineness characteristics, light-weight and canbe down-sized. A typical flat panel display (FPD) apparatus are liquidcrystal display apparatus, plasma display apparatus, and electronsemission type image display apparatus. Further, field emission displayapparatus (hereinafter called FED) have been in the spotlight. The FEDuses small cold cathodes that can be integrated

The FED comprises a rear substrate equipped with the above-said electronsources and a front substrate having a fluorescent material layer andanodes for forming electric fields (acceleration voltage) to cause theelectrons come from electron sources thereby to run into the fluorescentmaterial layer. These rear and front substrates are oppositely bonded toform a space between the substrates and the space is evacuated to aspecified vacuum status.

Japanese Patent Laid-open No. 2000-206905 (Patent literature 1)discloses a sealing method to form a high-vacuum space by using frameglasses. A typical well-known bonding material to hermetically sealelectronic parts is a glass material prepared by mixing a glass thatcontains PbO as the main ingredient with a filler whose coefficient ofthermal expansion is low. However, since lead (Pb) is poisonous,lead-free glasses have been widely used. Japanese Patent Laid-open No.2003-192378 (Patent literature 2) discloses a lead-freelow-melting-point glass for glass sealing. Patent literature 2 disclosesthe use of a glass that contains B₂O₃ or V₂O₅ and BaO in place of aPbO-B₂O₃ glass that may cause environmental pollution. Japanese PatentLaid-open No. 2004-250276 (Patent literature 3) discloses a sealingglass that contains V₂O₅, ZnO, BaO, and TeO₂.

Patent literature 1: Japanese Patent Laid-open No. 2000-206905

Patent literature 2: Japanese Patent Laid-open No. 2003-192378

Patent literature 31: Japanese Patent Laid-open No. 2004-250276

Sealing glasses containing lead (PbO as a starting material) have beenused widely. However, the water resistance of the sealing glass of a lowmelting point is low. For example, the surface of a part sealed by alead-containing glass is corroded in a few minutes in the air of 85° C.and 85% RH. Accordingly, the sealed part of a high-vacuum space may becorroded in the surfaces that are in contact with the atmosphere and thevacuum may be weakened. Similarly, lead-free sealing glasses are notresistant to water, either. Further, if the sealing glass is kept at ahigh sealing temperature for long time, the glass becomes easilycrystallized and less flowable. In extreme cases, bonding may bedisabled.

Meanwhile, V₂O₅—TeO₂ glass has a large coefficient of thermal expansion.Therefore, when the V₂O₅—TeO₂ glass is used for bonding, the glass mustbe mixed with a great quantity of the filler such as zirconium tungstenphosphate (ZWP) whose coefficient of thermal expansion is extremely low.Since there are not so much fillers to be selected and a great quantityof the filler of the low coefficient of thermal expansion is admixed,part or whole of melted glass will be crystallized. In other words, theglass is apt to be devitrified. When devitrified, the glass loses itssealing fluidity and cannot fit in the whole bonded area. Consequently,the glass cannot accomplish the sealing purpose.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to solve the aboveproblems and to provide an image display apparatus that uses a sealingglass containing substantially no lead, having a high bonding strengthand a long-life high-reliability by preventing reduction in vacuum ofthe vacuum space.

The present invention provides a display apparatus comprising a rearsubstrate and a front substrate wherein the substrates are oppositelyplaced to form a space therebetween and peripheral portions of thesubstrates are hermetically sealed with bonding material to keep thesealed space vacuumed. To solve the above problems, the image displayapparatus of the present invention is characterized by using a glassbonding material for sealing that contains at least a transition metal,phosphorous, barium, and antimony. It is preferable that the bondingmaterial is a mixture of filler and a glass that contains vanadium andphosphorous as the main ingredients. The above glass is characterized inthat the glass is a vanadate-phosphate glass containing V₂O₅ of 45 to60%, P₂O₅ of 15 to 30%, BaO of 5 to 25%, and Sb₂O₃ of 5 to 25% (byweight) in converted values as oxides.

The transition metal and phosphorus are ingredients for constituting astructure of the glass. Ba and Sb are elements for changing propertiesof the glass. The inventors found that the water- andmoisture-resistances of glasses containing phosphorus were improved byadding Ba and Sb in specified quantities or ratios. Particularly, it ispreferable that the glass contains 15 to 35% of BaO and Sb₂O₃ (inconverted valued as oxides) and the ratio by weight of BaO to Sb₂O₃ orSb₂O₃ to BaO is 0.3 or less. The ratios mean that the ratio of BaO toSb₂O₃ is in a range of 0.3 or less, and 3.3 or more.

Representative transition metal ingredients are vanadium and tungsten.It is preferable to appropriately add Ag, Cu, Cs, Hf, Na, K or Te to theabove sealing glass. The sealing temperature of the glass can be loweredby mixing these elements with the glass. The preferable ratio ofrespective elements in the glass is 10% by weight or less as the oxide.

The bonding material is a mixture of filler and a vanadate-phosphateglass that contains V₂O₅ as the main ingredient. The composition of theingredients in the glass is V₂O₅ of 45 to 60%, P₂O₅ of 20 to 30%, BaO of5 to 15%, TeO₂ of 0 to 10%, Sb₂O₃ of 5 to 10%, and WO₃ of 0 to 5% (byweight). The filler is at least one selected from the group consistingof silica glass, mullite, ceramic, fireclay refractory, steatite,alumina and spinel; the particle size of the filler is 1 to 150 μm; andan amount of the filler added to the glass is 80% by volume or less.

The use of the bonding material in accordance with the present inventioncan provide a display apparatus that has a sealing portion with a highbonding strength, high durability, and high yield. Further, the bondingmaterial in accordance with the present invention has an advantage ofavoiding environmental pollution due to lead and reduction of vacuum dueto devitrification in the sealing process. Furthermore, since thebonding material in accordance with the present invention can improvethe water- and moisture-resistances of the sealed areas, the reductionof vacuum due to deterioration of the sealing portion can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structure of FED, wherein FIG. 1A is a perspectiveview of an FED apparatus and FIG. 1B is a sectional view taken on lineA-A of FIG. 1A.

FIG. 2 is a magnified view of part of the cross-sectional schematic viewtaken on line A-A of FIG. 1A.

FIG. 3 is a partially broken schematic plane view for explaining thestructure of a flat-panel display apparatus of FIG. 1.

FIG. 4 is a detailed perspective view of the whole structure of theflat-panel display apparatus of FIG. 1.

FIG. 5 is a cross-sectional view taken on line of A-A′ of FIG. 4.

FIG. 6 is a graph showing the effect of lowering the glass softeningpoint of the sealing glass in accordance with the present invention.

FIG. 7 is a cross-sectional view showing a rib of the plasma display towhich the glass of the present invention is applied.

FIG. 8 is a cross-sectional view of glass beads and filler added to thesealing glass of the present invention.

FIG. 9 is a schematic diagram of the structure of a test piece forevaluation of the bonding strength of the glass.

FIG. 10 is a drawing to explain the method of the bonding strengthevaluation test.

PREFERRED EMBODIMENTS OF THE INVENTION

First, below will be explained the structure of a display apparatus inaccordance with the present invention. A flat panel display apparatuscomprises a front and rear substrate, which are oppositely arranged toform a space therebetween and the peripheral portions of the substratesare hermetically sealed with bonding material to make a unified vacuumspace. The outer surface of the front substrate is the display surfaceof the display apparatus. The rear substrate equipped with electronsources and the front substrate is covered with a fluorescent materialthat is excited to emit light by electrons emitted from the electronsources. A space of about 3 to 5 mm wide is provided between the frontand rear substrates and must be kept in a vacuum status. For thispurpose, it is possible to provide a marginal frame on the internal rimsof the front and rear substrates to thereby bond the frame to thesubstrates with a bonding material.

The front and rear substrates are bonded by a sealing glass directly orwith a marginal frame (sealing frame) or the like between thesubstrates. The marginal frame must be made of glass (as a frame glass).It is preferable to bond the frame glass respectively to the rearsubstrate and to the front substrate. When the rear substrate is flatand the front substrate has a unified marginal frame, the rear-surfaceend of the marginal frame (that is opposite to the rear surface) isbonded to the rear substrate with the sealing glass.

Electron sources available to the rear substrate can be a field emissiontype electron source (FE type), spin type electron source, surfaceconductance electron source (SED type), carbon nano-tube type electronsource, and thin-film type electron source such as MIM(Metal-Insulator-Metal) type, MIS (Metal-Insulator-Semiconductor), ormetal-insulator-semiconductor-metal type. Well-known FE type electronsources are a spin type made of metal such as molybdenum and asemiconductor substance such as silicone and a CNT type that uses carbonnano-tubes as electron sources. A unit picture element (pixel) is madeof a pair of electron sources array (a plurality of electron sources)and a fluorescent material array (a plurality of fluorescent materials.Usually, a single color picture element (pixel) consists three colorunit pixels: red (R), green (G), and blue (B). As for a color pictureelement, each of the unit picture elements is also called a sub-pictureelement (sub-pixel).

The rear substrate has a lot of metal foil lines that are connected toan electron source array to transfer selection signals and display dataon the inner surface of the substrate. Lines formed on the rearsubstrate or lines formed on the rim of the inner surface of the frontsubstrate can be used to feed electricity to the acceleration electrodeson the inner surface of the front substrate. At least one end peripheryof each substrate is provided with a line area for lines that are drawnto the rim. The peripheries of the substrates that contain the aboveline areas are bonding areas where the substrates are bonded to theother member with a sealing glass with lines between them.

The lines that are formed on the rear or front substrate are usuallymade of aluminum, silver, copper, chromium, or alloy thereof. Further,the lines can also use a lamination of these metals (for example, aCr—Al—Cr lamination). Chromium Cr is highly wettable to glasses andpreferable as a line material formed on the bonding area. The lines canbe made of a metal film that is prepared by a film-forming technology.Further, the sealing glass of the present invention contains noingredient that may corrode the lines containing Au and Ag.

Also judging from a viewpoint of line corrosion prevention, the presentinvention can provide a high corrosion-resistance image displayapparatus.

It is also possible to use members (spacers) that are called “partitionwalls” to support the front and rear substrates to keep an appropriateclearance (space) between the substrates. The spacer is a plate-likemember made of glass or ceramic that is a little conductive. The spacersare appropriately placed for each predetermined number of pixels so asnot to interfere with pixel operations.

To facilitate a sealing work in forming a vacuum space in the imagedisplay apparatus, a glass frit that is prepared in a form of flakes orpowder of the bonding glass into flakes or powder is recommended. Theglass frit is used as a glass paste by dispersing the frit into asolvent such as ethanol or water and mixing it with a binder such as anorganic compound. The glass paste can be made liquid when further mixedwith a solvent. The binder is used to keep the shape of the glass pastewhen the paste is applied and dried. Amounts of the solvent and binderadded to the glass paste can be changed, but usually an amount of thesolvent is 20 to 30% and an amount of the binder is 10% or less (to thetotal weight of the paste). In actual sealing, the glass frit isprepared by mixing the above glass flakes or powder with various kindsof particles (filler or beads) whose melting point is higher than thatof the sealing glass.

FIG. 1 is a general structure of FED. FIG. 1A is a perspective view of aFED apparatus. FIG. 1B is a sectional schematic view taken on line A-Aof FIG. 1A.

FIG. 2 is a magnified view of part of the sectional schematic view takenon line A-A of FIG. 1A.

Symbols are as follows:

101 Spacer

115 Conductive bonding layer

201 Rear substrate

202 Front substrate

203 Frame glass

204 Seal bonding layer

211 Rear substrate

212 Signal line

213 Scanning line

214 Electron sources

207 Display area

221 Front substrate

222 Light-shielding film (black matrix)

223 Anode

224 Fluorescent material layer

As seen in these drawings, rear substrate 201 has signal line (datalines and cathode electrode lines) 212 and scanning line (gate electrodeline) 213 on the inner surface of rear substrate 211. Electron source214 is formed near a point at which a signal line and a scanning linecross each other. Front substrate 202 has light-shielding film (blackmatrix) 222, anode (metal back) 223, and fluorescent material layer 224on the inner surface of front substrate 221.

Frame glass 203 is provided on the inner peripheries of rear substrate211 and front substrate 221. The frame glass is bonded to the front andrear substrates with the glass bonding material of the present inventionto form sealing bonding layer 204. An insulating film (not shown in thefigure) is formed on a surface where the rear substrate is bonded to theframe glass of the front substrate. With this, a space part is formedbetween the rear substrate and the front substrate. The space part iskept in a high vacuum status and works as display area 207. In FED,spacers 101 are disposed between scanning lines 213 that are formed onthe inner surface of rear substrate 211 and light-shielding film (blackmatrix) 222 that is formed on the inner surface of front substrate 221and bonded to the panel with conductive bond layer 115.

Rear substrate 211 and front substrate usually use glasses as theirmaterials. The front substrate uses a transparent glass.

In FED, the height-to-width ratio of seal bond layer 204 shouldpreferably be 0.06 to 0.18. The width of seal bond layer 204 is thewidth of the marginal frame and usually be approx. 6 mm. The height is adistance between the marginal frame and the panel glass and thethickness of a part which is filled with the bonding material. If thethickness becomes smaller, the bonding part becomes more resistant toshearing stress and has greater bonding strength. If the thickness isgreater, the bonding part is apt to have cracks. When the bondingmaterial of the present invention is used and the height-to-width ratioof the seal bond layer is set in the range of 0.06 to 0.18, the bondingpart has a large bonding strength and is hard to have cracks.

When assembling FED, it is preferable to coat the surface of themarginal frame in advance with the glass bonding material of the presentinvention. The whole surface of the frame or only part of the framesurface to be bonded to the panel glass can be coated with the glassbonding material in advance.

Meanwhile, the glass bonding material of the present invention is alsoavailable to seal panel glasses of the plasma display (PDF). Somedisplay apparatus adopt a method of bonding two panel glasses at evenintervals without using such a marginal frame that is used in PDF. Insuch a case, the bonding material can contain glass beads that arealmost spherical as the filler. It is possible to make the thickness ofthe bonding part in a predetermined range corresponding to the sizes ofthe beads by dispersing the glass beads in the bonding part. PDFrequires an aggregate in the bonding material to keep the clearancebetween panels constant. Glass beads play the role.

The particle size of glass beads determines the thickness of the sealingpart. So the mean particle size of the glass beads should preferably bein the range of 50 to 200 μm. Particularly, it is preferable that theparticle size of the glass beads is in the range of 100 to 300 μm andthat the ratio of the minor axis to the major axis of the glass bead is0.8 or more. The rate of glass beads to be added to the bonding materialshould be so small as to give no influence to the coefficient of thermalexpansion of the bonding material, particularly in the range of 0.1 to1.0% by volume. Since an amount of the glass beads to the bondingmaterial is so small that the coefficient of thermal expansion of thebonding material will not be affected. It is not necessary to considerthe coefficient of thermal expansion of the glass beads. If possible,however, the coefficient of thermal expansion of the glass beads shouldpreferably be about the same as that of the filler. The glass beads havea higher melting point than that of the sealing glass so that beadparticles may not be deformed in the bonding process. So the glass beadsare usually made of silica or alumina particles. When the glass beadsare used, the accuracy of the height determined by the glass beads canbe kept if the particle size of the glass beads dispersed in the otherbonding material such as filler is small enough. For example, when thefront substrate and the rear substrate are oppositely bonded at theirperipheries with a clearance of 100 μm between the substrates, glassbeads should be those of 90 to 100 μm (equivalent to 90 to 100% of theclearance width) whose particle size and shape are accuratelycontrolled.

The filler is added to improve the characteristics of the bondingmaterial such as coefficient of thermal expansion, sealing temperature,electric resistance, and wettability to display components. It ispossible to control the rates (% by volume) of the filler to the sealingglass in a glass frit according to applications. However, the preferablerate can be 10 to 80% (by volume) of the filler and 20 to 90% of thesealing glass. A plurality of fillers of different properties (such ascoefficients of thermal expansion) can be used. Granular metal fillersand inorganic oxide fillers are available. Particularly, availableinorganic oxides are for example, SiO₂, ZrO₂, Al₂O₃, ZrSiO₄, cordierite,mullite, and eucryptite.

Some kinds of fillers can be mixed according to target characteristicsof bonding material. SiO₂ is effective to control the coefficient ofthermal expansion of the bonding material since the coefficient ofthermal expansion of SiO₂ is smaller than that of glass containingvanadium and phosphorus as the main ingredients. Al₂O₃ can control theviscosity of the bonding material and augment the bonding material toreduce its cost since the coefficient of thermal expansion of Al₂O₃ isapproximately equal to that of the glass that contains vanadium andphosphorus as the main ingredients. Further, it is possible to increasethe thermal conductivity of the bonding material and facilitate bondingby adding the filler whose thermal conductivity is higher than that ofthe sealing glass.

To prevent devitrification of the glass and to obtain bonding parts thatare uniform in quality, particle sizes of the fillers are significant.If the particle size of the filler is too small, active surfacesincrease and the bonding parts may be easily crystallized. Contrarily,if the particle size of the filler is too large, the filler may bedispersed uneven locally and the bonding material may not be uniform inquality. So the particle size of the filler should preferably be 0.5 μmor more but not exceeding 150 μm, and more particularly 1 to 50 μm.Further, by increasing an amount of the fillers of a small particlesizes or the quantity of the small filler, the bonding material becomeshigher in viscosity and will not be easily sucked into the vacuumedspace during bonding. Therefore, the particle size of the filler shouldpreferably be in the range of 1 to 10 μm and more particularly in therange of 1 to 5 μm.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Embodiment 1

Embodiments 1 to 3 are examples of increasing the water resistance ofthe bonding material and improving its durability. These embodimentswill be explained in detail referring to the drawings below. FIG. 3 is aschematic plane view to explain the structure of a flat-panel displayapparatus. This display apparatus example uses an MIM(Metal-Insulator-Metal) type electron source.

By the way, in addition to the display apparatus of this embodiment, thepresent invention can also be applied to various kinds of displayapparatus and field emission type display apparatus that use wire-formedglass plates such as electrons emission type that use thin-film electronsources and plasma display apparatus. Further, the present invention isnot limited to structural materials such as substrates for flat-paneldisplay apparatus and their bonding and vacuum-sealing material. Thepresent invention can also be applied to glass structural members forelectronic apparatus such as magnetic disk substrates and structuralmaterials in other technical fields.

FIG. 4 is a detailed perspective view of the whole structure of theflat-panel display apparatus of FIG. 3. FIG. 5 is a sectional view takenon line of A-A′ of FIG. 4.

Symbols are as follows:

SUB1 Rear substrate

SUB2 Front substrate

s (s1, s2, . . . sm) Scanning signal line

d (d1, d2, d3, . . . ) Image signal line

ELS Electron sources

ELC Connection electrode

AD Anode

BM Black matrix

PH (PH(R), PH(G), PH(B)) Fluorescent material layer

SDR Scanning signal line drive circuit

DDR Image signal line drive circuit

In FIG. 3, FIG. 4, and FIG. 5, image signal lines d (d1, d2, . . . dn)are formed on the inner surface of rear substrate SUB1. Scanning signallines s (s1, s2, s3, . . . sm) are formed transversely over the imagesignal lines. Electron sources ELS are power-supplied by scanning signallines s (s1, s2, s3, . . . sm) through the connection electrode ELC.Symbol VS indicates a vertical scanning direction.

Front substrate SUB2 is a little smaller than rear substrate SUB1. LinesdT that are lead-out terminals of image signal lines d and lines sT thatare lead-out terminals of scanning signal lines s are formed on the sideface of rear substrate SUB1 that protrudes from front substrate SUB2.Fluorescent material layers of three colors PH (PH(R), PH(G), and PH(B))are formed on the inner surface of front substrate SUB2. Anodes AD areformed on them. Anodes AD are made of an aluminum layer. In actualoperation, a voltage of approx. 2 kV to 10 kV is applied to anodes AD onthe front substrate.

In this structure, fluorescent materials PH (PH(R), PH(G), and PH(B))are partitioned by light-shielding layer (black matrix) BM. Althoughanode AD is shown as a solid electrode, it can be stripe electrodes thatare traverses scanning signal lines s (s1, s2, s3, . . . sm) to form thestripe electrodes separated for every pixel row. Electrons emitted fromelectron sources ELS are accelerated and bombarded to fluorescentmaterial layers PH (PH(R), PH(G), and PH(B)) that constitute sub-pictureelements. With this, the fluorescent material layer PH emits light of apredetermined color. The light is mixed with lights of colors fromfluorescent materials of the other sub-pixels to form a color image of apredetermined color.

As shown in FIG. 4 and FIG. 5, rear substrate SUB1 and front substrateSUB2 are bonded together with sealing frame MFL that surrounds andencloses the display area. The bonding of rear substrate SUB1, frontsubstrate SUB2, and sealing frame MFL is accomplished with glass sealingbonding material. As explained referring to FIG. 3, the inner surface ofrear substrate SUB1 that is enclosed in the sealing area contains aplurality of electron sources in a display area that comprises a matrixof image signal lines d (d1, d2, d3, . . . dn) and scanning signal liness (s1, s2, s3, . . . sm). Lines dT and lines sT are led out over thesealing area on which sealing frame MFL is placed.

Supplied power from anode lines AD runs to rear substrate SUB1 throughconductors that connect substrates (not shown in the drawing) and goesout as lead-out terminals (line) on appropriate part of rear substrateSUB1 over the sealing area on which sealing frame MFL is place.

This embodiment employs a method of positioning sealing frame MFL in thesealing area from which lines are led out between front substrate SUB2and rear substrate SUB1 and bonding the sealing frame with glass bondingmaterial F for sealing. The peripheries of the front substrate SUB2 andrear substrate SUB1 that are oppositely placed are sealed and fixed withsealing glass bonding material F so that the sealed space between thesubstrates may be isolated from the outside. This embodiment uses aglass frit as the sealing glass.

When the glass bonding material is used for sealing, the material isheated at approx. 450° C., for example. The sealing method comprisessteps of preparing a glass paste, applying the paste to the peripheriesof the substrate by a dispenser, drying the paste at approx. 250° C.,for example, to evaporate the solvent, temporarily baking the paste atapprox. 460° C. to burn away the binder and melt the glass, placing asealing frame (marginal frame) on the molten glass, baking thereof at450° C. to fix the sealing frame, evacuating gas from the inside of thevacuum space of the display apparatus down to a pressure of approx. 1μPa through exhaust pipe 303, and sealing up the exhaust pipe.

It is preferable that the bonding material to bond the marginal frame tothe front substrate is different from the bonding material to bond themarginal frame to the rear substrate in softening points. The bondingdisplacement of the marginal frame is hard to be caused when thesoftening point of the bonding material which bonds the marginal frameto the front or rear substrate is higher than the softening point of thebonding material which bonds the marginal frame to the other substrate,if bonding with the bonding material of the higher softening point isdone, followed by bonding the bonding material of the lower softeningpoint. It is also possible to use, as front substrate SUB2, a substratein the form of a bordered shallow dish whose rim is protruded and benttowards rear substrate SUB1 and sealing the front and rear substrates atthe rim at which the substrates touch each other. In this case, thesealing glass is applied only to the rim of the rear substrate.

When spacers SPC are fixedly provided to keep an even clearance in thesealed space between the front and rear substrates, it is preferable toapply the sealing glass of this embodiment to areas at which spacers SPCare bonded to the front and rear substrates. As already explained, thisis because the glass of this embodiment is hard to releases moistureinto the vacuum. Usually, spacers SPC are disposed over scanning signallines s.

Table 1 lists examples of glass bonding materials for sealing to explaincompositions and characteristics of the sealing glass bonding materialsof the embodiment. Table 1 lists glass samples SPL-01 to SPL-30 becausethey differ in rates of ingredients. The content of each ingredient isgiven percentage by weight (wt %) of its converted values as oxides. Thestarting materials are V₂O₅ (Kojundo Chemical Lab. Co., Ltd.; Purity of99.9%), BaCO₃ (Kojundo Chemical Lab. Co., Ltd.; Purity of 99.9%), P₂O₅(Kojundo Chemical Lab. Co., Ltd.; Purity of 99.9%), and Sb₂O₃ (Wako FineChemicals Co., Ltd; Purity of 99.9%). Sample SPL-28 is almost the sameas sample SPL-27 in composition but SPL-28 uses barium phosphate insteadof P₂O₅ as a P supply source. The other starting materials are V₂O₅,BaPO₃, and Sb₂O₃. TABLE 1 Thermal characteristics Coefficient of Waterresistance 2 h thermal Transition (70° C.) Sample Ingredients (% byweight) expansion point Softening Before After name V₂O₃ P₂O₅ BaO Sb₂O₃Others (x10⁻⁷/° C.) (° C.) point (° C.) test (g) test (g) SPL-01 45 1520 20 78.5 403 485 0.837 0.835 SPL-02 45 20 20 15 77.6 410 496 0.8210.818 SPL-03 45 30 15 10 79.0 415 515 0.722 0.720 SPL-04 45 40 10 5 79.3422 520 0.710 0.687 SPL-05 45 50 3 2 78.5 435 535 0.774 0.739 SPL-06 4515 5 35 78.3 401 483 0.736 0.732 SPL-07 45 20 5 30 77.4 408 494 0.7520.752 SPL-08 45 30 5 20 78.8 413 512 0.737 0.737 SPL-09 45 40 5 10 79.1420 517 0.746 0.741 SPL-10 45 50 5 0 78.3 433 532 0.699 0.686 SPL-11 4515 35 5 84.8 413 497 0.706 0.699 SPL-12 45 20 30 5 83.8 420 508 0.7800.780 SPL-13 45 30 20 5 85.3 425 527 0.782 0.782 SPL-14 45 40 10 5 85.6432 532 0.744 0.740 SPL-15 45 50 0 5 84.8 445 548 0.759 0.726 SPL-16 5415 15 16 SPL-17 54 20 10 16 85.2 355 437 0.760 0.718 SPL-18 54 25 10 1186.3 358 438 0.754 0.750 SPL-19 54 30 5 11 84.9 362 445 0.713 0.707SPL-20 54 35 5 6 85.0 366 461 0.720 0.687 SPL-21 54 15 5 26 SPL-22 54 205 21 84.6 345 415 0.794 0.794 SPL-23 54 25 4 17 85/7 348 426 0.820 0.820SPL-24 54 30 3 13 84.3 352 433 0.824 0.824 SPL-25 54 35 0 11 84.4 356448 0.861 0.736 SPL-26 54 15 26 5 SPL-27 54 20 21 5 87.1 375 460 0.6900.690 SPL-28 54 20 21.6 4.4 98.9 360 435 0.689 0.689 SPL-29 54 25 17 488.2 378 463 0.811 0.811 SPL-30 54 30 13 3 86.8 382 470 0.718 0.718SPL-31 54 35 11 0 86.9 386 487 0.715 0.641 SPL-32 65 15 10 10 SPL-33 6520 5 10 SPL-34 65 25 5 5 77.0 316 395 0.765 0.570 SPL-35 65 30 2 3 78.2325 409 0.777 0.612 SPL-36 65 35 0 0 79.0 330 425 0.704 0.419 SPL-37 6515 4 16 SPL-38 65 20 3 12 SPL-39 65 25 2 8 76.2 314 392 0.782 0.698SPL-40 65 30 1 4 77.4 323 406 0.744 0.632 SPL-41 65 15 16 4 SPL-42 65 2012 3 SPL-43 65 25 8 2 78.5 321 401 0.760 0.682 SPL-44 65 30 4 1 79.8 330415 0.754 0.592 HPL-1 55 0 10 10 TeO₂ = 25 144.5 290 355 0.885 0.786Water resistance 2 h Constant-temperature constant-humidity (70° C.)test (in the air of 85° C., 85% RH) Weight Weight Sample change BeforeAfter change Sample name rate (%) test (g) test (g) rate (%) appearanceSPL-01 0.167 1.000 0.995 0.500 Δ SPL-02 0.355 1.020 1.012 0.784 Δ SPL-030.400 1.000 0.988 1.200 Δ SPL-04 3.330 1.000 0.900 10.000 X SPL-05 4.5001.050 0.950 9.524 X SPL-06 0.565 1.060 1.042 1.698 Δ SPL-07 0.000 1.0001.000 0.000

SPL-08 0.000 1.020 1.019 0.098 ◯ SPL-09 0.666 1.000 0.980 2.000 Δ SPL-101.861 1.020 0.963 5.588 X SPL-11 0.977 1.030 1.015 1.456 Δ SPL-12 0.0001.051 1.051 0.000

SPL-13 0.000 1.000 0.999 0.100 ◯ SPL-14 0.499 1.000 0.985 1.500 Δ SPL-154.323 1.040 0.905 12.981 X SPL-16 SPL-17 5.550 1.020 0.850 16.667 XSPL-18 0.453 1.030 1.016 1.359 Δ SPL-19 0.900 1.060 1.042 1.698 Δ SPL-204.562 1.000 0.863 13.700 X SPL-21 SPL-22 0.000 1.002 1.002 0.000

SPL-23 0.000 1.030 1.030 0.000

SPL-24 0.000 1.020 1.019 0.098 ◯ SPL-25 14.552 1.000 0.563 43.700 XSPL-26 SPL-27 0.000 1.020 1.020 0.000

SPL-28 0.000 1.000 1.000 0.000

SPL-29 0.000 1.000 1.000 0.000

SPL-30 0.000 1.050 1.049 0.095 ◯ SPL-31 10.390 1.000 0.688 31.200 XSPL-32 SPL-33 SPL-34 25.500 1.000 0.455 54.500 X SPL-35 21.245 1.0000.362 63.800 X SPL-36 40.500 1.020 0.000 100.000 X SPL-37 SPL-38 SPL-3910.715 1.010 0.685 32.178 X SPL-40 15.000 1.000 0.588 41.200 X SPL-41SPL-42 SPL-43 10.284 1.020 0.705 30.882 X SPL-44 21.479 1.000 0.35564.500 X HPL-1 11.232 1.050 0.150 85.714 X

To prepare samples of the sealing glass bonding materials, startingmaterials were mixed in weight rates listed in Table 1.

Considering that BaCO₃ is finally decomposed into BaO and CO₂, theweight of BaCO₃ was calculated as an equivalent amount to BaO. Allstarting materials excluding P₂O₅ were mixed in advance. This is becauseP₂O₅ is highly hygroscopic and its weight changes quickly by absorptionof moisture from the air when P₂O₅ is left in the open air for a longtime. The mixture of the starting materials excluding P₂O₅ was put in aplatinum crucible, and the platinum crucible was placed on a balance, Arequired amount of P₂O₅ was weighed and mixed with the powder mixture inthe platinum crucible on the scale with a metallic spoon; andimmediately mixed up the materials in the crucible. In this case, it ispreferable that a mortar and a ball mill for mixing are not used toavoid absorption of moisture from the atmosphere.

The platinum crucible containing the powder mixture of the materials wasplaced in a glass melting furnace, followed by starting heating at aheat-up rate of 5° C./min, and keeping the target temperature for onehour after the temperature reaches the target temperature. Thisembodiment sets the target temperature to 1000° C. The molten mixturewas stirred for one hour, followed by taking out the platinum cruciblefrom the glass melting furnace, casting the molten mixture into agraphite mold that is kept at 300° C. in advance, moving the graphitemold with the molten mixture into the unstraining furnace which was keptat a predetermined unstraining temperature, leaving the crucible in thefurnace for one hour to unstrain the glass, and cooling the crucibledown to the room temperature at a cooling rate of 1° C./min. Theobtained glass block is 30 mm×40 mm×80 mm. The glass block was crushedinto pieces of 4 mm×4 mm×15 mm each, and the coefficient of thermalexpansion (α), glass transition point (Tg), and glass softening point ofeach glass piece were measured and evaluated. The water resistance testand the constant temperature and humidity test were conducted on eachglass piece of the same shape. In preparation of glass samples, samplesSPL-16, 21, 26, 32, 33, 37, 38, 41, and 42 were not preparedsuccessfully since their ratios of phosphorus to vanadium were not inthe vitrification range. It is preferable that the rate (% by weight) ofV₂O₅ is 45 to 60 and the rate (% by weight) of P₂O₅ is 15 to 30.

A water resistance test method is performed is shown in the following.

Water of 100 cc at 70° C. was put in a 200-cc beaker; one weighed glasspiece of this embodiment was put in the beaker; the beaker was placed ina double boiler of 70° C.; the beaker was kept at 70° C. for 2 hours;the glass piece was taken out and dried on a heater at 150° C. for 30minutes, and measured the weight of the dried glass piece. The weightchange of the glass sample was calculated by the following expression:

A rate of change in weight of the glass sample before and after thewater-resistance test=(weight of glass piece before water-resistancetest−weight of glass piece after water-resistance test)/weight of theglass piece before water-resistance test×100 (%).

The constant-temperature and constant-humidity test method is shownbelow.

Each glass piece was ground into powder, followed by preparing a moldedform of 1 gram, placing it on a soda glass substrate, and baking it at450° C. for 30 minutes in the atmosphere to obtain a simulation sample.Then, the simulation sample was put in a thermostat chamber, followed bykeeping it in the humid air of 85° C. and 85% RH for 48 hours, washingthe tested sample in an ultrasonic washer to completely remove glassingredients that were effectually decomposed and dissociating and dryingthe tested glass piece on a heater at 150° C. for 30 minutes. Similarlyto the above-described water-resistance test, the weight change of theglass piece was calculated by the following expression:

A rate of change in weight of the glass sample before and after theconstant-temperature and constant-humidity test=(weight of glass pieceafter constant-temperature and constant-humidity test−weight of glasspiece before constant-temperature and constant-humidity test)/weight ofglass piece before constant-temperature and constant-humidity test×100(%). We evaluated the tested glass pieces by appearance and classifiedthem as follow:

Evaluation “⊚”: The rate of change in weight of this glass sample beforeand after the test is 0.1% or less. This tested glass sample is glossyas ever and no appearance change is found on the surface of the glasssample.

Evaluation “◯”: The rate of change in weight of this glass sample beforeand after the test is 0.1% or less. However, the tested glass sample isless glossy.

Evaluation “Δ”: The rate of change in weight of this glass sample beforeand after the test is 0.1% or more but not exceeding 5.0%.

Evaluation “x”: The rate of change in weight of this glass sample beforeand after the test is 5.0% or more.

Table 1 shows the results of evaluation of glass samples after the waterresistance test and the constant-temperature and constant-humidity test.

As for samples SPL-01, 02, 03, 06, 09, 11, 14, 18 and 19, the rate ofchange in weight of respective glass samples is 1% or less when kept inhot water of 70° C. for 2 hours. As for samples SPL-07, 08, 12, 13, 22,23, 24, 27, 28, 29, and 30, which are in accordance with the embodiment,no change was found in weight of respective glass samples after thetest. Judging from the result of the water resistance test, if the totalratio of Ba and Sb is smaller than 15% and over 35%, water resistance ofthe glass sample is not so good.

Judging from the results of the constant-temperature andconstant-humidity test, we find that glass samples SPL-2, 3, 4, 9, 14,17, 18, and 19 whose amount (BaO+Sb₂O₃) is 15 to 35 wt % and theBaO/Sb₂O₃ or Sb₂O₃/BaO ratio by weight is not 0.3 or less are relativelyresistant to water and can be used as a sealing glass bonding materialalthough the samples are a little deteriorated in theconstant-temperature and constant-humidity condition. Accordingly, theresults of evaluation of glasses of the embodiment after theconstant-temperature and constant-humidity test are all “⊚” or “◯”

By the way, the test results of samples SPL-28 and SPL-16 are almost thesame although their starting materials are partially different and theirevaluations after the constant-temperature and constant-humidity testare “⊚.” As comparative examples, sample HPL-1 that contains TeO₂wasprepared and evaluated. After the constant-temperature andconstant-humidity test, HPL-1 lost its gloss and changed its color toyellowish dark green. This indicates that HPL-1 is deteriorated byhumidity.

Although the above examples use vanadium as a transition metal which isone of the main ingredients of the glass, glass samples using tungstenas a transition metal can produce the similar effect.

Accordingly, these glass bonding materials enable sealing and bonding inhigh-humidity atmosphere.

Embodiment 2

To lower the melting point of the glass bonding material in accordancewith the present invention, various additive materials were searched andstudied. The compositions of SPL-27 as a representative sample wereselected in the above embodiment. Ag₂O, Cu₂O, Cs2_(o), HfO₂, Na₂O, K₂Oand/or TeO₂ was added to the powder mixture of glass materials whilechanging the rates of the added compound, and checked how their glasstransition points changed. As seen from FIG. 6 which lists the testresults, we found that additives of Ag₂O, Cu₂O, Cs₂O, HfO₂, Na₂O, K₂O,and TeO₂ respectively have an effect to lower the transition point ofthe glass bonding material in accordance with the present invention. Bythe way, when the additives are added too much, crystals are depositedin the glass. Accordingly, it is preferable that the rate (% by weight)of the additives is 1 to 10%. It is assumed that, when an additivematerial is added too much, the relative ratios of vanadium andphosphorus becomes lower and go beyond the vitrification range andconsequently crystals are deposited in the glass.

Embodiment 3

FIG. 7 is a cross-sectional schematic diagram to explain the structureof a plasma display apparatus.

The plasma display apparatus of Embodiment 3 of this invention isequipped with rear substrate SUB1 and front substrate SUB2 which areoppositely faced and bonded at their peripheries with bonding material Fthat uses the glass composition of this embodiment. The front substrateis equipped with discharge electrodes H and the rear substrate isequipped with address electrodes A. These electrodes are protected by aprotective layer. Rib spacers SPC are disposed among pixels and work aspartition walls to keep an appropriate clearance (space) between thefront and rear substrates. Each pixel contains fluorescent materials PHof three colors (red, green, and blue). This embodiment prepares theribs with a glass composition that satisfies the composition range of aglass bonding material that contains Ba and Sb of the above specifiedratios. This glass excels at resistance to water and moisture and itshygroscopic property is low. Accordingly, when this glass is used as amaterial for members in the vacuum space, this glass absorbs very littlemoisture during production and storage of the members and consequentlywill discharge almost no moisture when they are placed in a vacuumstatus. FIG. 8 shows a modification of the embodiment that adds glassbeads B and filler f are added to bonding material F. Since the glassbeads dispersed in the bonding material have almost the same diameters,the thickness of bonding material can be made constant over the wholeapparatus.

In the production of the plasma display apparatus, the vacuum spaceformed between the front and rear substrates is temporarily heated,evacuated, and then filled with a rare gas. The glass of this embodimentis also available in the evacuating process for evacuating the vacuumspace (that is provided for image displaying) during heating since theglass composition has a low hygroscopic property. Further, the panelswill not be deteriorated even when the panels are temporarily storedbefore or after the evacuating process.

Embodiment 4

Embodiments 4 to 6 explain the bonding materials, which improves thebonding strength and other properties of the bonding materials bycontrolling addition of fillers. The glass bonding materials ofEmbodiment 4 can be produced by adding a filler powder to avanadate-phosphate glass, which is a base material of the glass. First,below will be explained the base material of the glass of Embodiment 4.Then will be explained bonding of a member with a glass bonding materialto which a filler is added and mixed.

In production of a display apparatus, two glass panels must behermetically sealed. In production of FED, a marginal frame is placed onthe peripheries of two glass panels and bonded the bonding material. Thecoefficient of thermal expansion of glass plates such as widely-usedsoda glass and glass whose main component is silica in the range of 70to 80×10⁻⁷/° C. Therefore, the coefficient of thermal expansion of thebonding material should preferably be close to that of the glass panel.Further, the bonding material should have a high bonding strengthwithout causing devitrification in the sealing process.

The coefficient of thermal expansion of a vanadate-phosphate glasscontaining V₂O₅ as the main ingredient is 90×10 ⁻⁷/° C. or less and inmost cases, in the range of 60 to 90×10⁻⁷/° C. when the rates ofingredients are V₂O₅ of 45 to 60%, P₂O₅ of 20 to 30%, BaO of 5 to 15%,TeO₂ of 0 to 10%, Sb₂O₃ of 5 to 10%, and WO₃ of 0 to 5% (by weight).Since the coefficient of thermal expansion of the glass can be madesmaller, a selection of the filler materials to be added to the glassbecomes wider thereby to make the coefficient of thermal expansion ofthe glass closer to that of the sealing glass. Consequently, we canselect ceramics that has a stable property. Further, since this canreduce the quantity of fillers to be added, the devitrification of theglass can be suppressed. It is necessary to keep the above amounts ofthe ingredient so as to produce the glass of a coefficient of thermalexpansion in the range of 60 to 90×10⁻⁷/° C. or less.

Compounds V₂O₅ and P₂O₅ in the vanadate-phosphate glass (that is a glassbase material) work as ingredients to produce glass. Compounds BaO,TeO₂, Sb₂O₃ and WO₃ work to control the properties of the glass such ascoefficient of thermal expansion, fluidity, and the softening point. TO₂has an effect of lowering the melting point of the glass and the sealingtemperature.

Since the coefficient of thermal expansion of the above glass bondingmaterial is small, the above glass bonding material can be successfullyused as a filler material if its coefficient of thermal expansion is60×10⁻⁷/° C. or less. Practically, it is preferable to select a fillermaterial from a group of silica glass, mullite, ceramic, fireclayrefractory, steatite, alumina and spinel that are stable in properties.

When a glass is used as a bonding material for sealing, it is preferablethat the vanadate-phosphate glass of the glass base material has anelectric resistivity of 10⁸ Ω·cm or more and a coefficient of thermalexpansion in the range of 60 to 90×⁻⁷/° C. It is also preferable thatthe filler has a coefficient of thermal expansion of 60×10⁻⁷/° C. orless, a rate is 80% or less (by volume), and a particle size is 1 to 150μm. This can be accomplished by the above glass bonding material.

In the production of the glass base material, the starting materials areV₂O₅ (Kojundo Chemical Lab. Co., Ltd.; Purity of 99.9%), P₂O₅ (KojundoChemical Lab. Co., Ltd.; Purity of 99.9%), BaO (Wako Fine Chemicals Co.,Ltd.; Purity of 99.9%), Sb₂O₃ (Kojundo Chemical Lab. Co., Ltd.; Purityof 99.9%), WO₃ (Wako Fine Chemicals Co., Ltd.; Purity of 99.9%), andTeO₂ (Wako Fine Chemicals Co., Ltd.; Purity of 99.9%). Table 2 shows theingredient compositions (% by weight) of V₂O₅—P₂O₅ seal glasses.

In preparation of any glass samples, it is necessary to mix all startingmaterials excluding P₂O₅ in advance. This is because P₂O₅ is highlyhygroscopic and its weight changes quickly by absorption of moisturefrom the air when P₂O₅ is left in the open air for a long time. Steps ofpreparing the glass samples comprise putting the powder mixture of thestarting materials excluding P₂O₅ in an alumina crucible, placing thecrucible on the scale, weighing a required quantity of P₂O₅ in thecrucible on the scale, and immediately mixed up the materials in thecrucible with a metallic spoon. In this case, it is not preferable touse a mortar or a ball mill for mixing.

The following steps comprise putting the aluminum crucible with thepowder mixture of the materials in a glass melting furnace, starting toheat at a heat-up rate of 5° C./min, and keeping the target temperaturefor one hour after the temperature reaches the target temperature. Thisembodiment sets the target temperature to 1000° C. Further, thefollowing steps include keeping stirring the molten mixture for onehour, taking out the crucible from the glass melting furnace, castingthe molten mixture into a graphite mold that is kept at 300° C. inadvance, moving the graphite mold with the molten mixture into theunstraining furnace which was kept at a predetermined unstrainingtemperature, leaving the crucible in the furnace for one hour tounstrain the glass, and then cooling the crucible down to the roomtemperature at a cooling rate of 1° C./min. The obtained glass block is30 mm×40 mm×80 mm. The above steps are repeated to prepare the otherglasses of compositions listed in Table 2. TABLE 2 No. V₂O₅ P₂O₅ BaO WO₃TeO₂ Sb₂O₃ TAS-1 45 30 10 0 5 10 TAS-2 50 25 10 5 0 10 TAS-3 55 25 9 0 56 TAS-4 55 20 5 0 15 5 TAS-5 55 25 5 0 5 10 TAS-6 52 22 5 8 5 8 TAS-7 5025 15 0 5 5 TAS-8 65 15 10 0 5 5 TAS-9 57 22 5 0 8 8 TAS-10 58 22 5 0 78 TAS-11 60 20 6 0 6 8

After measuring the surface resistance of the obtained glass block, theglass block was cut into pieces of 4 mm×4 mm×15 mm each, and measuredand evaluated the coefficient of thermal expansion of the glass pieces.Further, the residual glass material was crushed into glass powder andperformed DTA analysis on the glass powder. Table 3 lists the physicalproperties of the prepared V₂O₅-P₂O₅ seal glass. In Table 3, symbolsindicate the following: Tg for glass transition point, Mg for yieldingpoint, Ts for softening point, and Tf for fluidity point. Theappropriate sealing temperature is between Ts (glass softening point)and Tf (glass fluidity point).

It is possible to change the coefficient of thermal expansion of theglass in the range of 60 to 90×10⁻⁷/° C. by changing the glasscomposition as shown in Table 3. It is possible to lower the sealingtemperature by adding a little amount of TeO₂ to the glass. TAS-4, 6,and 8 contain a large amount of TeO₂, WO₃ or V₂O₅. Therefore, theircoefficients of thermal expansion exceed 90×10⁻⁷/° C. and cannot be inthe range of 60 to 90×⁻⁷/° C. or less. TABLE 3 Crystalli- CoefficientCrystallization zation peak of thermal Tg Mg Ts Tf temperaturetemperature expansion No. (° C.) (° C.) (° C.) (° C.) (° C.) (° C.)(×10⁻⁷/° C.) TAS-1 345 370 420 475 515 530 66 TAS-2 350 375 430 485 526541 75 TAS-3 370 395 445 495 537 552 84 TAS-4 345 365 425 480 520 536103 TAS-5 340 365 425 480 520 536 82 TAS-6 345 360 435 505 548 563 95TAS-7 345 365 420 480 520 536 82 TAS-8 345 354 415 495 537 552 98 TAS-9335 343 403 480 521 536 82 TAS-10 325 333 390 466 505 520 79 TAS-11 315323 379 452 490 504 77

TAS-1 was selected from V₂O₅—P₂O₅ glasses listed in Table 2, and afiller material and glass beads were added to TAS-1. Both the fillermaterial and glass beads are silica glasses. We evaluated the fluidityof powder mixture of the glass material and behavior of crystallizationof the glass material since the glass of this invention is used forsealing.

To evaluate the fluidity of glass materials, we employed a button flowtest to evaluate the fluidity of powder mixture of the glass material.The button flow test comprises the steps of placing button-shaped heapsof the sealing frit powder on a non-sealing glass plate, heating thereofuntil they melt, and measuring the diameters of the molten button-shapedglass materials. At the same time, the reactivity of the glass material(sample) with the substrate, occurrence of cracks in the substrate, andgeneration of gas bubbles in the molten glass sample were investigatedduring this test. The glass sample were acceptable when thebutton-shaped glass sample of 10 mm in diameter and 5 mm thick spreadsout to have a diameter of 15 mm or more and has no crack and gas bubblesbetween the substrates.

The button flow test method is shown in the following.

Samples TASF-1 to TASF-18 that were molded into button-like shapes wereplaced on a sealed glass substrate at room temperature, followed byheating them at a rate of 5° C./min, keeping them at 420° C. for 30minutes, cooling them down to 200° C. at a rate of 2° C./min, andleaving them still until the temperature reached to room temperature.

Table 4 lists the results of the button flow test.

The tested samples were evaluated as follows:

(As for the fluidity of the glass)

Evaluation “⊚”: The button sample spread out and its diameter is 15 mmor more. There is no crack between the sample and the substrate and nogas bubble is found in the sample.

Evaluation “◯”: The button sample spread out and its diameter is 15 mmor more.

Evaluation “x”: The diameter of the molten button sample is less than 15mm.

(As for the crystallization behavior)

Evaluation “⊚”: No crystal peak is found by the X-ray diffractionanalysis of the sample surface after the button flow test. The surfaceof the sample is found to be glossy (with the naked eye observation).

Evaluation “◯”: No crystal peak is found by the X-ray diffractionanalysis of the sample surface after the button flow test but thesurface of the sample is not glossy partially (by the naked eyeobservation).

Evaluation “x”: Some crystal peaks are found by the X-ray diffractionanalysis of the sample surface after the button flow test.

The glass sample that is evaluated “x” in the crystallization behaviortest is devitrified.

Judging from the above test results, the preferable particle size of thefiller is in the range of 1 to 150 μm. Further, it was not preferable toadd the filler in a too much amount to the glass bonding material and apreferable mixing rate of the filler is 0.1 to 1.0% by volume of thebonding material. TABLE 4 Particle Mixing rate Particle size Mixingratio size of filler of filler of glass bead of glass beads FlowCrystallization Number (d90) (μm) (% by volume) (μm) (% by volume)characteristics behavior TASF-1-1 1 20 50 0.5 ◯ ◯ TASF-1-2 1 40 50 0.5 ◯◯ TASF-2-1 5 10 100 0.5

TASF-2-2 5 20 100 0.5

TASF-3-1 10 20 150 0.5

TASF-3-2 10 40 150 0.5

TASF-4-1 20 30 200 0.5

TASF-4-2 20 60 200 0.5

TASF-5-1 50 10 50 0.5

TASF-5-2 50 20 50 0.5

TASF-6-1 100 20 100 0.5

◯ TASF-6-2 100 40 100 0.5

◯ TASF-7-1 150 30 150 0.5

◯ TASF-7-2 150 60 150 0.5

◯ TASF-8-1 180 10 200 0.5 ◯ X TASF-8-2 180 20 200 0.5 ◯ X TASF-9-1 21020 50 0.5 X X TASF-9-2 210 40 50 0.5 X X TASF-10-1 300 30 100 0.5 X XTASF-10-2 300 60 100 0.5 X X TASF-11-1 10 10 150 0.1

TASF-11-2 10 20 150 0.1

TASF-12-1 10 20 200 0.2

TASF-12-2 10 40 200 0.2

TASF-13-1 10 40 50 0.5 X X TASF-13-2 10 80 50 0.5 X X TASF-14-1 10 10100 0.7

◯ TASF-14-2 10 20 100 0.7

◯ TASF-15-1 10 20 150 1 ◯ ◯ TASF-15-2 10 40 150 1 ◯ ◯ TASF-16-1 10 30200 1.5 ◯ X TASF-16-2 10 60 200 1.5 ◯ X TASF-17-1 10 10 100 2 X XTASF-17-2 10 20 100 2 X X TASF-18-1 10 20 200 2.5 X X TASF-18-2 10 40200 2.5 X X

The bonding strengths of the bonding materials containing the fillersand glass beads that were prepared by Embodiment 1. FIG. 9 is anexplanatory drawing of a test piece of bonding material whose bondingstrength is to be evaluated.

FIG. 10 is an explanatory drawing of a strength evaluation test whichuses a test piece of FIG. 9.

As shown in FIG. 9, test piece 300 for bonding strength evaluationcomprises first part 310 of width w1×height h1×thickness d1 and secondpart 320 of width w2×height h2×thickness d2 which are bonded together toform a T-shape. In details, dimensional values are as follows: w1=25 mm,w2=15 mm, h1=50 mm, h2=20 mm, d1=2.8 mm, and d2=2.8 mm. The bondinglocation of second part 320 (the distance of the second part from thetop end of the first part) is 15 mm.

The bonding strength test uses a test piece prepared by inserting thefree end of first part 310 that is bonded to test piece 300 (for bondingstrength evaluation) of FIG. 10A into the groove of sample holder 330 ofFIG. 10B. FIG. 11C shows an image of the bonding strength test. Thefirst part is tightly fastened by a screw which is screwed into thescrew hole. Sample holder 330 is anchored to base 340. FIG. 10(c)contains top and side views of the test piece.

As shown in FIG. 10C, pusher 350 is pushed against the second part oftest piece 300 that is bonded to sample holder 330 to apply load W tothe second part. Load W is gradually increased until the bonded part ofthe test piece is broken and the load (W) is measured when the bondedpart is broken. The test results are listed in Table 5. Table 5 alsolists breaking stresses of the well known Pb glasses and V—Te glassesthat contain V₂O₅ and TeO₂ as the main ingredients for comparison.

Judging from the results of the strength measurement, the breakingstress and the bonding strength go down when the particle size of fillerbecomes over 150 μm. The breaking stress is apt to go down as the amountof the filler to be added increases. Further, the breaking stress is notaffected when the ratio of glass beads to be mixed is 1.0% or less (byvolume), but both the breaking stress and the bonding strength go downwhen the amount of the glass beads to be mixed becomes over 1.5% (byvolume). TABLE 5 Particle size Mixing ratio Particle size Mixing ratioBreaking stress of filler of filler of glass bead of glass beads ofbonding Number (d90) (μm) (% by volume) (μm) (% by volume) material(MPa) TASF-1-1 1 20 50 0.5 75.5 TASF-1-2 1 40 50 0.5 64.2 TASF-2-1 5 10100 0.5 70.8 TASF-2-2 5 20 100 0.5 60.2 TASF-3-1 10 20 150 0.5 61.5TASF-3-2 10 40 150 0.5 52.3 TASF-4-1 20 30 200 0.5 46.7 TASF-4-2 20 60200 0.5 39.7 TASF-5-1 50 10 50 0.5 55.3 TASF-5-2 50 20 50 0.5 47.0TASF-6-1 100 20 100 0.5 60.8 TASF-6-2 100 40 100 0.5 51.7 TASF-7-1 15030 150 0.5 48.1 TASF-7-2 150 60 150 0.5 40.9 TASF-8-1 180 10 200 0.532.0 TASF-8-2 180 20 200 0.5 27.2 TASF-9-1 210 20 50 0.5 28.9 TASF-9-2210 40 50 0.5 24.6 TASF-10-1 300 30 100 0.5 Not bonded TASF-10-2 300 60100 0.5 Not bonded TASF-11-1 10 10 150 0.1 62.5 TASF-11-2 10 20 150 0.153.2 TASF-12-1 10 20 200 0.2 58.6 TASF-12-2 10 40 200 0.2 49.8 TASF-13-110 40 50 0.5 45.1 TASF-13-2 10 80 50 0.5 38.3 TASF-14-1 10 10 100 0.757.7 TASF-14-2 10 20 100 0.7 49.0 TASF-15-1 10 20 150 1 63.2 TASF-15-210 40 150 1 53.7 TASF-16-1 10 30 200 1.5 43.6 TASF-16-2 10 60 200 1.537.1 TASF-17-1 10 10 100 2 42.3 TASF-17-2 10 20 100 2 36.0 TASF-18-1 1020 200 2.5 39.5 TASF-18-2 10 40 200 2.5 33.6 Conventional 65.5 material(Pb glass) Conventional 67.3 material (V-Te glass)

1. A display apparatus comprising a rear substrate equipped with aplurality of electron sources and a front substrate equipped with aplurality of fluorescent materials wherein the substrates are oppositelyplaced to form a space therebetween and peripheral portions of thesubstrates are hermetically sealed with a bonding material to keep thesealed space under a reduced pressure; wherein the bonding material is amixture of a filler and a glass that contains vanadium and phosphorousas main ingredients and the glass is a vanadate-phosphate glass thatcontains V₂O₅ of 45 to 60%, P₂O₅ of 15 to 30%, BaO of 5 to 25%, andSb₂O₃ of 5 to 25% (by weight) in converted values as oxides.
 2. Adisplay apparatus comprising a rear substrate equipped with a pluralityof electron sources and a front substrate equipped with a plurality offluorescent materials wherein the substrates are oppositely placed toform a space therebetween and the peripheral portions of the substratesare hermetically sealed with bonding material to keep the sealed spaceunder a reduced pressure; wherein the bonding material is made of aglass that contains at least vanadium, phosphorous, barium, andantimony; and amounts of the ingredients are 15 to 35% of BaO and Sb₂O₃in total in converted values as oxides and a ratio of BaO to Sb₂O₃ orSb₂O₃ to BaO is 0.3 or less.
 3. The display apparatus according to claim2, wherein the bonding material contains 20 to 90% (by volume) of aglass ingredient and 10 to 80% (by volume) of filler.
 4. The displayapparatus according to claim 3, wherein the filler is at least oneselected from the group consisting of SiO₂, ZrO₂, Al₂O₃, ZrSiO₄,cordierite, mullite, and eucryptite and a mean particle size thereof is0.5 to 10 μm.
 5. The display apparatus according to claim 2, wherein theglass contains 45 to 60% (by weight) of V₂O₅ in a converted value asvanadium oxide and 15 to 30% (by weight) of P₂O₅ in a converted value asphosphorous oxide.
 6. The display apparatus according to claim 2,wherein a marginal frame is provided between the front and rearsubstrates.
 7. The display apparatus according to claim 2, wherein thebonding material contains glass beads by 0.1 to 1.0% (by volume) of thebonding material whose particle size is 90 to 100% of a distance of thespace between the front and rear substrates.
 8. The display apparatusaccording to claim 2, wherein the front substrate has a peripheral rimthat is curved and protruded towards the rear substrate, the front andrear substrates therewith being bonded to each other.
 9. The displayapparatus according to claim 2, wherein the glass contains at least oneof Ag, Cu, Cs, Hf, Na, K and Te as an additive by 1 to 10% by weight ina converted value as oxides of Ag₂O, Cu₂O, Cs₂O, HfO₂, Na₂O, K20 andTeO₂.
 10. The display apparatus according to claim 1, wherein the glassis a vanadate-phosphate glass that contains V₂O₅ of 45 to 60%, P₂O₅ of20 to 30%, BaO of 5 to 15%, TeO₂ of 0 to 10%, Sb₂O₃ of 5 to 10%, and WO₃of 0 to 5% (by weight); the filler is at least one selected from thegroup consisting of silica glass, mullite, ceramic, fireclay refractory,steatite, alumina and spinel, a particle size of the filler is 1 to 150μm, and an amount of the filler added to the glass is 80% by volume orless.
 11. The display apparatus according to claim 10, wherein acoefficient of thermal expansion of the vanadate-phosphate glass is in arange of 60 to 90×10⁻⁷/° C. and a coefficient of thermal expansion ofthe filler is 60×10⁻⁷/° C. or less.
 12. The display apparatus accordingto claim 11, wherein the bonding material is mixed with glass beads of50 to 200 μm in size and the glass beads dispersed in the filler is 0.1to 1.0% by volume.
 13. The display apparatus according to claim 11,wherein the coefficient of thermal expansion of the glass beads is60×10⁻⁷/° C. or less.
 14. The display apparatus according to claim 11,wherein the display apparatus is a field emission type display that isequipped with two glass substrates one of which has the electron sourcesthat emit electrons and the other of which is equipped with thefluorescent material that receive electrons to be excited therebyemitting light.
 15. The display apparatus according to claim 11, whereinthe display apparatus is a plasma display apparatus.
 16. A plasmadisplay apparatus equipped with a front substrate and a rear substratethat is provided oppositely to the front substrate and partition wallsthat are formed on the rear substrate to provide a space between thefront and rear substrates, wherein the partition walls are made of aglass that contains at least vanadium, phosphorous, barium and antimonyand an amount of ingredients contained in the glass are 15 to 35% of BaOand Sb₂O₃ in total by weight and the ratio by weight of BaO to Sb₂O₃ orSb₂O₃ to BaO is 0.3 or less.